Magnetic loudspeaker



Nov. 22, 1960 E. A. HEPPNER 2,961,497

MAGNETIC LOUDSPEAKER Filed May 1, 1957 United States Patent MAGNETICLOUDSPEAKER Elmore A. Heppner, Round Lake, Ill., assignor to HeppnerManufacturing Co., a corporation of Illinois Filed May 1, 1957, Ser. No.656,289

4 Claims. (Cl. 179-114) This invention relates to a magnetic loudspeakerand in particular to loudspeakers utilizing a reed for vibrating thecone.

It is the principal object of the invention to provide a new andimproved reed type inducer for use in a speaker wherein the reed isresiliently centered between opposed pole pieces.

Another object is to provide such an inducer wherein the reed is clampedat one end between a pair of magnets and the pole pieces are arranged toform with the reed and the magnets a pair of magnetic loops wherein theflux components in the reed tend to cancel each other.

A further object is to provide such an inducer having a fixed coilassociated with the pole pieces and arranged around the reed to inducemagnetic flux in the reed thereby to displace the reed from the centeredposition between the pole pieces as an incident to the passage of asignal current through the coil.

Still another object is to provide such an inducer wherein the coil iscenter-tapped for use with an audio frequency signal providing circuit,whereby direct current may be fed into the center tap to pass throughopposed coil windings thereby to have a mutual counteracting eflect andpreclude affecting the reed.

Other features and advantages of the invention will be apparent from thefollowing description taken in connection with the accompanying drawingswherein:

Fig. 1 is a rear view of a loudspeaker having an inducer embodying theinvention;

Fig. 2 is, a side view thereof; and

Fig. 3 is a section view thereof taken approximately along the line 33of Fig. 1.

In the exemplary embodiment of the invention as disclosed in thedrawings, a loudspeaker generally designated is shown to comprise aframe 11 arranged to carry in the conventional manner a diaphragm orcone 12. The invention comprehended herein relates to the means forvibrating the cone to produce sounds corresponding to an electricalsignal. More specifically, this means, herein referred to as transducer13, comprises a magnetic reed device responsive to an input signal ofaudio frequency to produce a corresponding mechanical displacement ofthe cone 12.

Reference being had more specifically to Fig. 3, transducer 13 is seento comprise a pair of magnets 14 and 15 between which one end 16a of anelongated, fiat reed 16 is clamped. The magnets are preferably of thebar type and are arranged so that the north pole of one magnet and thesouth pole of the other magnet are in abutment with reed end 16a. Whileit makes no difference which of the two possible arrangements isemployed, for illustrative purposes I have shown the first magnet 14 ashaving its south pole 14a and the second magnet 15 as having its northpole 15a in opposed abutment with reed end 16a. Further, while magnets14 and 15 may be alternatively of the permanent or electromagnetic typeas desired, they are illustrated herein as comprising permanent magnetsformed of a material having suitable high magnetic flux characteristicssuch as the alloy Alnico V. The means for clamping the magnets is shownto comprise a stud 17 which is arranged to be secured to a brace 18carried on frame 11, for securing the entire transducer 13 to the frame.

. Reed 16 is preferably formed of a resilient or springy sheet materialpermitting high flux density. One example of a material found to beparticularly satisfactory for such purposes is the iron-cobalt alloymanufactured under the trade name Permendur.

Extending from outer or north pole portion 14b of magnet 14 is a firstpole piece 19 having an end 19a spaced a slight distance away from asecond portion 16b of the reed. A similar second pole piece 20 extendsfrom the outer or south pole portion 15b of magnet 15 with an end 20aspaced a slight distance from reed portion 16b opposite end 19a of thefirst pole piece. Thus, an air gap 21 is formed between pole piece ends19a and 20a in which reed portion 16b is centered. Pole pieces 19 and 20are preferably formed of a material such as soft iron having lowreluctance. As best seen in Fig. 3 the pole pieces are secured to themagnets by means of stud 17.

The above described arrangement of the magnets, pole pieces and reedresults in the formation of two magnetic circuits or loops. The firstsuch loop is one wherein the fiux leaves the north pole 14b of the outermagnet 14, passes through pole piece 19, and through the reed fromportion 16b to end portion 16a, and returns to the magnet at south pole14a. The second loop is one wherein the flux leaves the north pole 15aof magnet 15, passes through reed 16 from end 16a to portion 16bthereof, and through pole piece 20, and returns to the magnet at southpole 15b thereof. Magnets 14 and 15 are of equal magnetic strength andthus the flux components in the reed cancel each other. The reed portion16b is retained by its resiliency in a centered position between poleends 19a and 20a in a magnetically neutral condition.

An input electrical signal is caused to act upon reed 16 by means of acoil 22 extending freely around the reed and disposed between the polepiece ends 19a and 20a and the magnets. The coil is carried on asuitable bobbin 22a which s slightly smaller internally in a directionperpendicular to the fiat plane of the reed than the distance betweenpole piece ends 19a and 20a. Thus the reed movement through gap 21 islimited by abutment of the reed with the bobbin, thereby precluding thereed from contacting either pole piece end. When an electrical signalsuch as an audio frequency current passes through coil 22, it magnetizesthe reed in a manner corresponding to the amplitude and direction of thecurrent. The varying magnetic flux induced in portion 16b of the reedreacts with the magnetic field between ends 19a and 20a of the polepieces to cause the reed to be drawn alternatively to one or the otherof the pole pieces and away from the centered position. At the outer endof the reed, a pin 23 is provided to connect fixedly the apex 12a ofcone 12 and the reed. Thus the movement of reed portion 16b in the gap21 causes end 16c of the reed to move pin 23 and the cone 12 at thefrequency of and in correspondence with the amplitude of the inputsignal.

While coil 22 may be of any suitable type proper for use with thespecific audio frequency signal supply circuit to be used, in theillustrated embodiment, the coil comprises a continuous coil having afirst end connection 22b, a center-tap connection 22c and a second endconnection 22d. Thus direct current from the power supply may be fedinto the coil center-tap connection 22c from which it may flow inopposite directions to each of the end connections 22a and 220.Resultingly, the magnetizing effect of the direct current on reed 16 iscanceled out and only the alternating, audio frequency current which issupplied through end connections 22b and 22d affects the reed. Suchacoil arrangement is advantageous where push-phil circuits are employedfor "providing the audio frequency current. V

While Ihave shown and descrihed cet'tain embodiments of my invention, itis to be understood that iscapable of many modifications. Changes,ther'efot e, ii1 theconstruction and arrangement may be iriade withoutdeparting from the spirit and scope of the'i'nvention as defined in theappended claims.

I claim: V p

1. A transducer comprising: a reed bf readily nag netizable material; apair of pole pieces spaced on appesite sides ofone 'portion of the reed;apair of magnets for inducing flux in said pole pieces to form oppositepoles therein adjacent the feed, said magnets and pole pieces extendingin a series relationship to place another portion of the reed in amagnetically neutral condition; and a coil forindu'cing in said reed amagnetic flux corresponding to an alternating current signal, said coilbeing center tapped for distributing direct current through oppositehalves of the coil in opposite directions to nullify magnetic effectthereof on said reed.

2. A transducer comprising: an elongated reed of resilient materialhaving a high permeability; a firstrnagn'et having a north pole abuttinga first portion of the reed; a first pole piece extending from the southpole of said magnet to an end spaced slightly from a second portion ofthe reed to form with the reed and first magnet a first magnetic loop; asecond magnet similar to the first magnet and having a south poleabutting said first portion of the reed opposite the north pole of saidfirst magnet, whereby said first portion is clamped therebetween; asecond pole piece extending from the north pole of the second magnet toan end spaced slightly from said second reed portion opposite the end ofthe first pole piece to form with the reed and second magnet a secondmagnetic loop, the resiliency of said reed acting to urge said secondportion of the reed to a centered position in an air gap formed betweensaid ends of the pole pieces; and a coil around said reed to magnetizesaid second portion in conformity With electrical current therein, tocause corresponding displacement of said second portion relative to saidcentered position, said coil having opposing portions for carrying adirect current component of the signal in opposite directions to nullifyits effect on said reed.

3. A speaker comprising: a reed of resilient material adapted to havehigh flux saturation; at first permanent magnet having a north poleadjacent a first portion of the reed; a first soft iron pole pieceextending from the south pole of said magnet to an end spaced slightlyfrom a second portion of the reed to form with the reed and first magneta first magnetic loop; a second permanent magnet similar to the firstmagnet and having a south pole adjacent said first portion of the reedopposite the north pole of said first magnet; a second soft iron polepiece extending from the north pole of the second magnet to an endspaced slightly from said second portion opposite the end of the firstpole piece to form with the reed and second magnet a second magneticloop, whereby the fluxes in the reed cancel each other out, said secondportion of the reed being urged to a centered position intermediate saidends of the pole pieces by the resiliency of the reed; a coil aroundsaid reed to magnetize said second portion in conformity with an audiofrepuency electrical signal, to cause said magnetized second portion toreact with said pole piece ehds and be displaced relative to saidcentered position, said coil being center tapped to permit directcurrent to be fed therethrough without effecting the reed; a speakerdiaphragm; and means connecting the reed to the diaphragm to move saiddiaphragm with said second portion.

4. A transducer comprising: pole pieces forming a pair of spacedmagnetic poles of opposite polarity; a magnetic reed extending freelythrough the space between said poles and having a portion projectingtherefrom; a coil carried on an annular bobbin around said portion forinducing a magnetic flux in the element as a result of passage of audiofrequency c'urrent through the coil, said flux coacting with "the fluxof the magnetic poles to reciprocate the element toward and fromrespective poles, said bobbin being internallysmaller ina directionparallel to a line between the poles than the distance betweenthc polepieces thereby limiting the extentof reciprocation of the element topreclude contact of the'reed with each of said polepiece's.

References Cited in the file of this patent UNITED STATES PATENTS1,153,593 Baldwin a Sept. 14, 1915 2,241,107 Woodru'g May 6, 19412,300,638 Wente Nov. 3, 1942 2,551,114 Lavery June 13, 1950 2,582,942Baker Jan. 22, 1952 2,588,327 Roberts 'et a1. Mar. 4, 1952 2,692,918Berger t Oct. 26, 1954

